The present invention relates to an automatic change-over method for strip material.
In particular, the present invention relates to an automatic change-over method for strip material fed by a traction unit along a given path, the traction unit being located along the path and upstream, in the traveling direction of the strip material, from a cutting station where the strip material is cut transversely into pieces and along any cutting line.
The present invention is especially suitable for use on production machines employing strip material, e.g. semi-rigid paper, and particularly cigarette packing machines to which the following description refers purely by way of example.
Italian Patent Application n. 3426A/90, to which full reference is made herein in the interest of full disclosure, relates to a strip material automatic change-over device whereby the end of a new strip is connected to a first run-out strip fed along an unwinding path by the traction roller unit of a user packing machine. The first strip is fed by the traction unit rollers to a cutting station located along said path and where the first strip is cut into pieces of desired shape along not necessarily straight cutting lines.
According to the above patent, a given end portion of the new strip is fed over and on to the first strip by which the new strip is drawn by friction through the traction unit and from there to the cutting station. When a cut is made in the overlapping portion of the two strips, the first cut in the new strip frequently corresponds with its end edge. Since the end edge of the new strip is normally straight and perpendicular to the longitudinal axis of the strip, and since, as already stated, the cutting line, as opposed to being straight and parallel to the end edge of the new strip, is frequently so shaped as to intersect the end edge at various points, the cut made in the overlapping portion of the two strips normally results in the formation of relatively small scraps which drop down into the bottom of the packing machine and require frequent stoppage of the machine for their removal.